In some mechanical fields, a seal must be effected between pieces of equipment. For example, one common application of sealing technology relates to creating a seal against a spinning shaft, such as the spinning shaft 10 depicted in FIG. 1A. As shown in FIG. 1B, it may be necessary to create a seal around the shaft 10 in order to prevent a fluid 15 present at one side of the shaft 10 from leaking around the shaft 10.
Accordingly, stuffing box 20 may be positioned around the shaft 10. The stuffing box 20 may include a packing material, referred to herein as a compression packing seal 30, which is wrapped around the rotating shaft and provides an interface and sealing surface between the rotating shaft 10 and the stuffing box 20. Thus, the fluid 15 is prevented from penetrating past the compression packing seal 30 and leaking to the atmosphere.
In some situations, a lantern ring 40 may be in communication with a shaft in the stuffing box 20. The lantern ring 40 may include a hole for delivering a fluid, such as a lubricating oil, from the channel to the rotating shaft 10.
The compression packing seal 30 may be in the form of a braided material, and is commonly square or round when viewed in cross section (although the compression packing seal 30 may be provided in a variety of cross-sectional shapes). The compression packing seal 30 may be cut to an appropriate size and wrapped around the shaft 10 to form a ring. Multiple rings of compression packing seal 30 may be provided along the length of the shaft 10 in order to provide a seal around the shaft 10. A packing gland 50 may be used to secure the compression packing seal(s) 30 inside the stuffing box 20 and compress the compression packing seal(s) around the shaft 10.
Typically, in order to form the compression packing seal 30, one or more materials are braided together in a braid pattern, such as a square pattern or a corner-reinforced pattern. The braiding patterns are realized by moving two or more materials along a series of material paths in an x-y plane, which builds up a braided structure that increases in size in a z-plane. FIGS. 2A-2D depict common braiding patterns (in the x-y plane) used in conventional compression packing seals.
For example, FIG. 2A depicts a braid known as a square braid, formed by braiding two materials along a two-tracked set of material paths 60. The result is a braided structure 70, shown in side-view in FIG. 2B, where the two materials alternate at each corner of the square.
FIG. 2C depicts a 3-track interbraided square structure, wherein three materials are braided along a three-tracked set of material paths 80. The result is a braided structure 90, shown in side-view in FIG. 2D, where the three materials alternate on each side of the square. FIG. 2E depicts a three-dimensional side-view perspective view of the braided structure 90 of FIG. 2D.
Similarly, FIG. 2F depicts a 4-track interbraided square structure, wherein one to four materials are braided along a four-tracked set of material paths 100 (most commonly, one material is used on all four paths). The result is a braided structure 110, shown in FIG. 2G, where the one to four materials alternate on each side of the square.
FIG. 2H depicts a special case of the 4-track interbraided square structure of FIG. 2F. In FIG. 2H, a four-tracked set of material paths 120 is provided. In this example, two materials are used in the four-tracked material paths. That is, the same material is repeated on two “internal” material paths, and a different material is repeated on the “external” material paths. Thus, the first material is present along the sides of the compression packing seal, while the second material is present in the corners of the compression packing seal, as shown in FIG. 2I.
Such a structure may be useful, for example, if the corners of the compression packing seal are expected to receive more wear than the sides. Thus, a sturdier material may be used to reinforce the corner sections, while a less expensive or more lubricating material may be used to fill in the sides.
FIG. 2J depicts an example of a braid-over-braid pattern. Specifically, the braid of FIG. 2J is formed by wrapping two symmetrical overbraids around a core.
FIG. 2K depicts a combination “end ring” useful for anti-extrusion purposes. For example, the end ring includes exterior braided rings (formed, e.g., from braided carbon fiber) and a series of interior rings. The interior rings may be, for example, molded graphite. In FIG. 2K, the interior rings are made of different materials, although this is not necessarily always the case. The exterior rings are useful for their anti-extrusion properties, while the interior rings provide a sealing surface.
A variety of types of materials may be used to form the compression packing seal, and properties of the stuffing box/shaft/fluid system may affect the requirements of the packing seal and therefore the materials employed in the compression packing seal.
However, the properties of the stuffing box/shaft/fluid system may not be evenly distributed, qualitatively or quantitatively, throughout the system. For example, the side of the packing seal that faces the shaft may be exposed to a large amount of wear-and-tear due to the rotation of the shaft, while the opposite side (which faces the stuffing box) may be subjected to significantly reduced stress. Further, the side of the seal in the corner of the stuffing box nearest to the fluid that is sealed against may need to have a greater resistance to extrusion, because at this location the seal must effect a seal with a gap between the bottom of the stuffing box and the shaft. There is not an extrusion concern on intermediate rings of the seal because there is not a need to seal across such a gap.
The conventional braiding patterns described above each suffers from shortcomings in addressing the above-noted problem. More specifically, the different materials of the braided structures tends to be distributed evenly around the entire braided structure. For example, as shown in the four-tracked structure 100 of FIG. 2C, each side of the 4-track interbraided square structure exposes all of the materials. Thus, it is difficult to deploy the 4-track interbraided structure so that only certain materials are exposed to certain conditions. For example, it is not possible for the 4-track interbraided structure to present one material chosen for durability on the side facing the shaft 10, and another inexpensive material on the side facing the stuffing box 20. Instead, all four materials are present facing every direction.